The objective of this study is to evaluate the safety, tolerance and pharmacokinetics of three doses (200 mg BID, 300 mg BID, and 400 mg BID) of oral voriconazole, compared to an (active) control (fluconazole at 400 mg/day), in patients with hematologic malignancies/conditions, solid tumors, or patients with autologous bone marrow transplants at risk for development of aspergillosis. This randomized, double-blind, active-controlled study will be conducted in up to three sequential phases, at three or more sites. In each phase of the study, a sufficient number of patients will be recruited in order to produce 12 evaluable cases. This study has just initiated patient accrual. For the purpose of this protocol, an evaluable case will be defined as follows: 1) a patient that has completed the full 14-day treatment period; or 2) a patient that has been discontinued because of a treatment-related adverse event.